diff --git a/packager/app/test/testdata/bear-320x240-vorbis-webm-golden.mpd b/packager/app/test/testdata/bear-320x240-vorbis-webm-golden.mpd
index d2fb244afc..8f8784be96 100644
--- a/packager/app/test/testdata/bear-320x240-vorbis-webm-golden.mpd
+++ b/packager/app/test/testdata/bear-320x240-vorbis-webm-golden.mpd
@@ -2,7 +2,7 @@
 <!--Generated with https://github.com/google/shaka-packager version <tag>-<hash>-<test>-->
 <MPD xmlns="urn:mpeg:dash:schema:mpd:2011" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xlink="http://www.w3.org/1999/xlink" xsi:schemaLocation="urn:mpeg:dash:schema:mpd:2011 DASH-MPD.xsd" xmlns:cenc="urn:mpeg:cenc:2013" profiles="urn:mpeg:dash:profile:isoff-on-demand:2011" minBufferTime="PT2S" type="static" mediaPresentationDuration="PT2.768S">
   <Period id="0">
-    <AdaptationSet id="0" contentType="audio">
+    <AdaptationSet id="0" contentType="audio" subsegmentAlignment="true">
       <Representation id="0" bandwidth="69362" codecs="vorbis" mimeType="audio/webm" audioSamplingRate="44100">
         <AudioChannelConfiguration schemeIdUri="urn:mpeg:dash:23003:3:audio_channel_configuration:2011" value="2"/>
         <BaseURL>output_audio.webm</BaseURL>
diff --git a/packager/app/test/testdata/bear-320x240-vp9-opus-webm-golden.mpd b/packager/app/test/testdata/bear-320x240-vp9-opus-webm-golden.mpd
index 8a22b035a1..4b34ee862f 100644
--- a/packager/app/test/testdata/bear-320x240-vp9-opus-webm-golden.mpd
+++ b/packager/app/test/testdata/bear-320x240-vp9-opus-webm-golden.mpd
@@ -2,7 +2,7 @@
 <!--Generated with https://github.com/google/shaka-packager version <tag>-<hash>-<test>-->
 <MPD xmlns="urn:mpeg:dash:schema:mpd:2011" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xlink="http://www.w3.org/1999/xlink" xsi:schemaLocation="urn:mpeg:dash:schema:mpd:2011 DASH-MPD.xsd" xmlns:cenc="urn:mpeg:cenc:2013" profiles="urn:mpeg:dash:profile:isoff-on-demand:2011" minBufferTime="PT2S" type="static" mediaPresentationDuration="PT2.741S">
   <Period id="0">
-    <AdaptationSet id="0" contentType="audio">
+    <AdaptationSet id="0" contentType="audio" subsegmentAlignment="true">
       <Representation id="0" bandwidth="75444" codecs="opus" mimeType="audio/webm" audioSamplingRate="48000">
         <AudioChannelConfiguration schemeIdUri="urn:mpeg:dash:23003:3:audio_channel_configuration:2011" value="2"/>
         <BaseURL>output_audio.webm</BaseURL>
@@ -11,7 +11,7 @@
         </SegmentBase>
       </Representation>
     </AdaptationSet>
-    <AdaptationSet id="1" contentType="video" width="320" height="240" frameRate="1000000/34000" par="16:9">
+    <AdaptationSet id="1" contentType="video" width="320" height="240" frameRate="1000000/34000" subsegmentAlignment="true" par="16:9">
       <Representation id="1" bandwidth="203360" codecs="vp9" mimeType="video/webm" sar="427:320">
         <BaseURL>output_video.webm</BaseURL>
         <SegmentBase indexRange="302-350" timescale="1000000">
diff --git a/packager/app/test/testdata/bear-640x360-vp8-cenc-webm-golden.mpd b/packager/app/test/testdata/bear-640x360-vp8-cenc-webm-golden.mpd
index fd1217f61b..0354738a2d 100644
--- a/packager/app/test/testdata/bear-640x360-vp8-cenc-webm-golden.mpd
+++ b/packager/app/test/testdata/bear-640x360-vp8-cenc-webm-golden.mpd
@@ -2,7 +2,7 @@
 <!--Generated with https://github.com/google/shaka-packager version <tag>-<hash>-<test>-->
 <MPD xmlns="urn:mpeg:dash:schema:mpd:2011" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xlink="http://www.w3.org/1999/xlink" xsi:schemaLocation="urn:mpeg:dash:schema:mpd:2011 DASH-MPD.xsd" xmlns:cenc="urn:mpeg:cenc:2013" profiles="urn:mpeg:dash:profile:isoff-on-demand:2011" minBufferTime="PT2S" type="static" mediaPresentationDuration="PT2.736S">
   <Period id="0">
-    <AdaptationSet id="0" contentType="video" width="640" height="360" frameRate="1000000/33000" par="16:9">
+    <AdaptationSet id="0" contentType="video" width="640" height="360" frameRate="1000000/33000" subsegmentAlignment="true" par="16:9">
       <ContentProtection schemeIdUri="urn:uuid:1077efec-c0b2-4d02-ace3-3c1e52e2fb4b" cenc:default_KID="31323334-3536-3738-3930-313233343536">
         <cenc:pssh>AAAANHBzc2gBAAAAEHfv7MCyTQKs4zweUuL7SwAAAAExMjM0NTY3ODkwMTIzNDU2AAAAAA==</cenc:pssh>
       </ContentProtection>
diff --git a/packager/app/test/testdata/bear-640x360-vp8-webm-golden.mpd b/packager/app/test/testdata/bear-640x360-vp8-webm-golden.mpd
index 4622bff4c9..f177a945ff 100644
--- a/packager/app/test/testdata/bear-640x360-vp8-webm-golden.mpd
+++ b/packager/app/test/testdata/bear-640x360-vp8-webm-golden.mpd
@@ -2,7 +2,7 @@
 <!--Generated with https://github.com/google/shaka-packager version <tag>-<hash>-<test>-->
 <MPD xmlns="urn:mpeg:dash:schema:mpd:2011" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xlink="http://www.w3.org/1999/xlink" xsi:schemaLocation="urn:mpeg:dash:schema:mpd:2011 DASH-MPD.xsd" xmlns:cenc="urn:mpeg:cenc:2013" profiles="urn:mpeg:dash:profile:isoff-on-demand:2011" minBufferTime="PT2S" type="static" mediaPresentationDuration="PT2.736S">
   <Period id="0">
-    <AdaptationSet id="0" contentType="video" width="640" height="360" frameRate="1000000/33000" par="16:9">
+    <AdaptationSet id="0" contentType="video" width="640" height="360" frameRate="1000000/33000" subsegmentAlignment="true" par="16:9">
       <Representation id="0" bandwidth="335457" codecs="vp8" mimeType="video/webm" sar="1:1">
         <BaseURL>output_video.webm</BaseURL>
         <SegmentBase indexRange="289-338" timescale="1000000">
diff --git a/packager/media/formats/webm/single_segment_segmenter.cc b/packager/media/formats/webm/single_segment_segmenter.cc
index ead19d3f99..29a6be7572 100644
--- a/packager/media/formats/webm/single_segment_segmenter.cc
+++ b/packager/media/formats/webm/single_segment_segmenter.cc
@@ -7,6 +7,7 @@
 #include "packager/media/formats/webm/single_segment_segmenter.h"
 
 #include "packager/media/base/muxer_options.h"
+#include "packager/media/event/muxer_listener.h"
 #include "packager/third_party/libwebm/src/mkvmuxer.hpp"
 
 namespace shaka {
@@ -31,6 +32,11 @@ Status SingleSegmentSegmenter::FinalizeSegment(uint64_t start_timestamp,
   CHECK(cluster());
   if (!cluster()->Finalize())
     return Status(error::FILE_FAILURE, "Error finalizing cluster.");
+  if (muxer_listener()) {
+    const uint64_t size = cluster()->Size();
+    muxer_listener()->OnNewSegment(options().output_file_name, start_timestamp,
+                                   duration_timestamp, size);
+  }
   return Status::OK;
 }